To prevent a collision accident at an intersection, between-road-and-vehicle communication is under study. In the between-road-and-vehicle communication, information related to an intersection situation is communicated between a road-side device and a vehicle device. In the between-road-and-vehicle communication, installation of the road-side device is necessary, which requires much working and cost. In contrast to this, in between-vehicles communication, that is, in a form of communicating information between vehicle devices, the installation of the road-side device becomes unnecessary. In this case, for example, the current location information is detected by means of a GPS (Global Positioning System) and the like, and the location information is exchanged between the vehicle devices, whereby it is determined on which roads one vehicle and the other vehicle are situated to enter an intersection (e.g., see a patent document 1).